No branch of zoning law is more perplexing than the constitutional limits of the police power. How severely may the government reduce the value of land by regulation without compensating the owner? This issue has become particularly prominent during the last decade, as state and local governments have sought to preserve the landscape by novel and sometimes stringent land-use controls. Recently, some scholars have suggested that the familiar “diminution-of-value” test for determining when regulations become unconstitutional should be abandoned, even in cases where the prohibited use is not akin to a nuisance, and the effect of the regulation is to render the tract worthless. In Just v. Marinette County, the Wisconsin Supreme Court seemed to adopt this idea, declaring that development of a shoreland marsh may be forbidden irrespective of the economic impact on the landowner. Naturally, such decisions create the impression that property owners are regularly being sacrificed for the sake of environmental quality. But a study of Just's origins and effects reveals that in Wisconsin and Minnesota this impression of regulatory zeal is inaccurate. As a rule, all four of the counties studied allowed owners of shoreland marshes to fill enough of the marsh to make a remunerative use of the tract. Their main concern was not to preserve marshes but rather to attach erosion-control conditions to the fill permits. Cases in which a county, by denying a fill permit, drastically reduced the value of the land, have been extremely rare, even in the three Wisconsin counties studied, where under Just such denials are clearly constitutionally permissible. In these counties, it appears that ideology and politics, not constitutional law, are the major factors limiting the severity of conservancy zoning and consequently the extent to which this technique preserves open space. In jurisdictions where this is so, it seems likely that judicial decisions that permit the government to prohibit all remunerative uses are more likely to rationalize unjust treatment of an occasional landowner than to make a major contribution toward preserving environmental quality.